Air quality conformity applies to long-range transportation plans, shorter-term transportation improvement programs (TIPs) and transportation projects funded or approved by the Federal Highway Administration (FHWA) or the Federal Transit Administration (FTA). Conformity requirements apply in areas that either do not meet or previously have not met certain air quality standards.

Conformity determinations must be made at least every three years, or when transportation plans or TIPs are updated. In addition, conformity determinations must be made within 12-months of an area being designated by Environmental Protection Agency (EPA) as nonattainment for ozone (O3), particulate matter (PM-2.5), or nitrogen oxides (NOx), the pollutants for which conformity is required.

Different regions throughout Ohio require conformity determinations, most of which lie within MPO boundaries. In these areas, the MPOs travel demand model must be used to forecast traffic that will be used in estimating future emissions due to vehicles.

Total regional emissions are calculated using the vehicle miles traveled (VMT) from the model output, and they are multiplied by emission rates (in grams/mile traveled). The emission rates are generated using the EPA’s MOVES (MOtor Vehicle Emissions Simulator) air quality model.

Another growing area of air quality involves analyses of Mobile Source Air Toxics (MSAT). Mobile source air toxics are compounds emitted from highway vehicles and non-road equipment which are known or suspected to cause cancer or other serious health and environmental effects. Emission rates for MSATs are also generated using the MOVES air quality model, and they are likewise used in conjunction with MPO travel demand models to estimate total pollutant levels.